RNA polymerase, figuratively known as the CPU in the cell, regulates the entire process of transcribing genetic information DNA into RNA. So far, there are 9 types of RNA polymerases in the three domains (bacterial domain, archaeal domain, and eukaryotic domain), among which the largest and most complex "chloroplast RNA polymerase" has not been successfully resolved, which is a major mystery to be solved in the scientific community for decades. Today, Chinese scientists have successfully solved this mystery. On March 1, the cover of the top international academic journal "Cell" was a structural diagram of "chloroplast RNA polymerase", and the cover article of this issue was "Structure of RNA Polymerase Cryo-EM Encoded by Plant Chloroplasts", which was completed by the research team of Zhang Yu of the Center for Excellence in Molecular Plant Science of the Chinese Academy of Sciences and the research team of Zhou Fei of Huazhong Agricultural University. In this study, the cryo-EM structure of the chloroplast gene transcription machine was analyzed, and the "assembly parts", "assembly modes" and "functional modules" of the chloroplast gene transcription machine were revealed.
The research results were published on the cover of the top international journal "Cell".
According to researcher Zhang Yu, photosynthesis in chloroplasts converts light energy into chemical energy, providing energy and oxygen for life on earth, and is an important shaper of the earth's environment. 1.5 billion years ago, prokaryotic cyanobacteria were swallowed up by eukaryotic cells and eventually evolved into today's plant chloroplasts. In this process, the genome genes of cyanobacteria are continuously transferred to the nucleus, eventually forming a "small but fine" chloroplast genome, but the machine for transcribing the chloroplast genome is not simple at all. On the basis of the prokaryotic cyanobacterial gene transcription machine, it is equipped with a number of unique functional modules, and then its "body shape" changes to the original 25 times, the number of "assembled parts" is 3 times the original. However, these modules have little "prototype" in prokaryotic cyanobacteria, and most of them are "borrowed" from eukaryotic cells. Years of research have shown that chloroplast gene transcription machinery controls the development process of chloroplasts and the gene expression of mature chloroplasts, and plays a key role in regulating plant photosynthesis, but the structure of chloroplast gene transcription machinery is still unknown.
In 2016, Zhang's research team began to challenge this global problem. "Chloroplast RNA polymerase is a unique CPU of plant cells, which regulates 80% of chloroplast genes and is responsible for the development and function of chloroplasts. If the structure of chloroplast RNA polymerase can be resolved, it will undoubtedly open the door to the field of chloroplast gene transcription. With his curiosity about nature and the spirit of inquiry, Zhang Yu persisted in exploring for 8 years. He said that the reason for perseverance is due to the atmosphere created by the Center for Excellence in Molecular Plant Science for many years, which allows young talents to concentrate on hard bones.
Chloroplast gene transcription protein machinery construction.
The research team first constructed chloroplast transgenic tobacco by chloroplast transformation technology, then obtained the complete chloroplast gene transcription protein complex by affinity purification, and finally successfully resolved the chloroplast gene transcription machine structure by single-particle cryo-electron microscopy. Compared with the prokaryotic cyanobacterial gene transcription machine, the chloroplast gene transcription machine has a total of 20 "assembly parts" (protein subunits), which are composed of five functional modules, including catalytic module, scaffold module, protection module, RNA module and regulatory module, among which the catalytic module is encoded by the chloroplast genome, and its protein subunit originates from cyanobacteria. Other modules are encoded by the nuclear genome, and most of their protein subunits originate in eukaryotic cells and are transported to chloroplasts for assembly after cytoplasmic translation. These protein subunits of prokaryotic and eukaryotic origin make up the most complex gene transcription machinery currently known.
The catalytic module of cyanobacteria** contains 6 protein subunits, which are located in the core layer of the complex; The scaffold module contains 7 protein subunits, which stabilize the catalytic module on the one hand, and provide binding sites for other modules on the other; The protection module includes 2 subunits, which function as superoxide dismutase, which protects them from oxidative attack by superoxide in chloroplasts; The RNA module includes one subunit, which can specifically bind RNA to the RNA and speculate that it may be involved in the RNA processing of transcriptional associations. The regulatory module includes 4 subunits, which are speculated to be involved in the regulation of the activity of gene transcription machinery.
Researcher Zhang Yu inspects samples in the laboratory.
Han Bin, academician of the Chinese Academy of Sciences and director of the Center for Excellence in Molecular Plant Science of the Chinese Academy of Sciences, believes that at the basic research level, this study has laid a foundation for further exploring the working mode of chloroplast gene transcription machinery, understanding the gene expression regulation mode of chloroplasts, and modifying the chloroplast gene expression regulatory network. This study provides a new idea for improving the gene expression level of the photosynthesis system, and is expected to improve the efficiency of plant photosynthesis and increase carbon sinks. In addition, at the level of synthetic biology applications, this research provides a starting point for improving the efficiency of plant chloroplast bioreactors, helping the production of recombinant vaccines, recombinant protein drugs, and natural products.
** in the article is provided by the Center for Excellence in Molecular Plant Science, Chinese Academy of Sciences).
* People's ** client Shanghai Channel |Written by Huang Xiaohui.
Edited by Gao Chenchen.
Process Editor: Ma Xiaoshuang.